Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-9-80 series airplanes, that currently requires inspection and replacement of certain suspect horizontal stabilizer primary trim motors. That AD was prompted by an analysis which revealed that certain incorrectly manufactured motor shafts could fail prematurely and, in turn, cause the primary trim motor to fail. The actions specified in that AD are intended to prevent such failures of the primary trim motor, which could ultimately result in reduced controllability of the airplane. This action would expand the applicability of the existing AD to include additional airplanes.